Vitamin D.sub.3, which is cholecalciferol, has been known for many years. It may be prepared from cholesterol by the introduction of an additional bond into the cholesterol molecule to produce 7-dehydrocholesterol and subjecting the 7-dehydrocholesterol to ultraviolet irradiation. It was at one time thought to be biologically active in the regulation of intestinal calcium transport and the mobilization of calcium from bone.
Recently, it has been discovered that to be biologically active the cholecalciferol has to be hydroxylated in the body to 25-hydroxycholecalciferol or certain derivatives thereof, and it is the 25-hydroxycholecalciferol and derivatives thereof which are active in regulating intestinal calcium transport and mobilization of calcium from bone. It would, therefore, be important to prepare and administer 25-hydroxycholecalciferol instead of Vitamin D.sub.3.
It is known that 25-hydroxycholecalciferol can be produced by ultraviolet radiation of its provitamin 25-hydroxy-7-dehydro-cholesterol but it has not heretofore been possible to obtain 25-hydroxycholesterol except in amounts so small as to make it impractical for use in the preparation of 25-hydroxycholecalciferol. The transformation of 25-hydroxycholesterol to 25-hydroxy-7-dehydrocholesterol and the preparation of 25-hydroxycholecalciferol from the 7-dehydro compound by irradiation with ultraviolet light was described by J. W. Blunt and H. F. DeLuca in Biochemistry 8, 671 (1969). The biological activity of the synthetic 25-hydroxycholecalciferol was also assayed by the same authors, and the results published in their paper.
Sources from which 25-hydroxycholesterol has been prepared in small amounts include: cholesterol, stigmasterol 3.beta.-hydroxypregn-5-ene (synthesized from a natural source) and ergosterol (from which 25-hydroxy-7-dehydrocholesterol may be obtained). Yields in these syntheses are usually poor, chemicals needed for carrying out the procedures may have to be specially prepared, and in some cases special equipment is required which may not be conveniently available in a plant producing industrial chemicals.
The synthesis of 25-hydroxycholesterol by E. J. Semmler, M. F. Holic, H. K. Schnoes and H. F. DeLuca (Tetrahedron Letters, 4147 (1972)) begins with the oxidation of cholesterol. The oxidation product is converted to i-homocholanic acid methyl ether which is esterified with diazomethane, a dangerous, explosive compound. Then by a number of steps a hydroxyl group is introduced into position 6. Without counting the preparation of i-homocholanic acid, 18 steps are required to introduce the hydroxyl groups. Further, the scarcity of the starting material makes the method impractical for large scale manufacture.
Accordingly, I have set about to discover a new synthesis of 25-hydroxycholecalciferol, and particularly a new synthesis of 25-hydroxy-7-dehydrocholesterol. I have sought such a synthesis for which a starting material is readily available and in which high yields of 25-hydroxycholesterol or 25-hydroxycholecalciferol may be obtained. Further, I have sought syntheses in which the chemicals necessary for conducting the necessary reactions are commercially available and reasonably priced and I have sought such syntheses which utilize equipment generally available in chemical manufacturing plants so as to avoid the need for large capital investments.